1. Field of the Invention
The present invention relates to a passive focus detection apparatus, for use with a single lens reflex camera, etc.
2. Description of the Related Art
Almost all of recent single lens reflex cameras are provided with a split pupil phase difference detection type of passive focus detection apparatus. In such a focus detection apparatus, it is important to increase the focus detection area with respect to the field of view formed by an objective lens (photographing lens). Various solutions for obtaining an increased focus detection area have been proposed. For example, it has been proposed to combine a plurality of line sensors or to use an area sensor in order to increase the focus detection area.
However, if a focusing operation is carried out on a portion wherein the focusing detection area is wide, i.e., on a portion wherein the image height of the object is high, a conjugate relationship between the exit pupil of the objective lens and the AF entrance pupil from a wide angle extremity to a telephoto extremity cannot be maintained, so that focus detection cannot be carried out at either the wide-angle extremity or at the telephoto extremity.
In theory, one solution to detect the focus at a high image height h, i.e., in a large object image area (focus detection area), and solve the above-mentioned problem is to fix the size and position of the exit pupil, that is, to restrict usable objective lenses. However, this solution cannot be applied to a single lens reflex camera in which various objective lenses, including zoom lenses of large zoom ratio, having different exit pupil positions and diameters are used.
It is an object of the present invention to provide a focus detection apparatus in which a large focus detection area can be provided, regardless of the exit pupil position and diameter of the objective lens.
To achieve the object mentioned above, according to the present invention, a focus detection apparatus is provided, including a pupil dividing device for dividing an exit pupil of an objective lens into separate areas; a field mask located at a position substantially optically equivalent to an image forming position of the objective lens; a condenser lens located in the vicinity of the field mask to make the exit pupil conjugate with the pupil dividing device; a light quantity distribution forming device for receiving light transmitted through the separate areas and forming light quantity distribution portions wherein the relative position of the light quantity distribution portions varies in accordance with a focus state of the objective lens; and a focus detection apparatus having at least one group of photoelectric transducers which receive the light quantity distributed by the pupil dividing device. The condenser lens is moved in accordance with the position of the exit pupil of the objective lens.
With this structure, since the condenser lens is moved in accordance with the position of the exit pupil of the objective lens, a light quantity distribution with sufficient quantity of light can be obtained to carry out a precise focus detection.
Preferably, the condenser lens includes a movable lens element which is moved along the optical axis thereof.
The condenser lens can include a plurality of lens elements which are relatively moved along the optical axis thereof.
The condenser lens can include a stationary lens element and a movable lens element, wherein the movable lens element is movable along the optical axis.
Preferably, the focus detection apparatus is provided in a single lens reflex camera, wherein the condenser lens is moved in accordance with the position of the exit pupil of a photographing lens mounted to the single lens reflex camera.
Preferably, the single lens reflex camera further includes a fine movement mechanism which drives the condenser lens in accordance with the position of the exit pupil via a controller.
The photographing lens can include a memory which stores position data of the exit pupil of the photographing lens, wherein the position data of the exit pupil is retrieved by the controller.
In an embodiment, the photographing lens includes a zoom lens; a memory, wherein the position data of the exit pupil is stored in the memory in accordance with a change in a focal length upon zooming of the zoom lens; and a focal length detecting device which detects the focal length which is changed upon zooming. The position data of the exit pupil is retrieved by the controller in accordance with the focal length detected by the focal length detecting device.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2000-185896 (filed on Jun. 21, 2000) which is expressly incorporated herein by reference in its entirety.